Any time you overlap two different glazes . . . you create a new, third glaze. And, depending on the contents of the two glazes, you could end up with an unstable/nondurgable glaze that leeches a coloring oxide, etc. Doesn't matter if the glazes were made by two different companies or the same company. Putting a "safe" clear over a "problem" glaze will not automatically make the resulting glaze safe . . . you need to test it.

Any time you overlap two different glazes . . . you create a new, third glaze. And, depending on the contents of the two glazes, you could end up with an unstable/nondurgable glaze that leeches a coloring oxide, etc. Doesn't matter if the glazes were made by two different companies or the same company. Putting a "safe" clear over a "problem" glaze will not automatically make the resulting glaze safe . . . you need to test it.

Any time you overlap two different glazes . . . you create a new, third glaze. And, depending on the contents of the two glazes, you could end up with an unstable/nondurgable glaze that leeches a coloring oxide, etc. Doesn't matter if the glazes were made by two different companies or the same company. Putting a "safe" clear over a "problem" glaze will not automatically make the resulting glaze safe . . . you need to test it.

Any time you overlap two different glazes . . . you create a new, third glaze. And, depending on the contents of the two glazes, you could end up with an unstable/nondurgable glaze that leeches a coloring oxide, etc. Doesn't matter if the glazes were made by two different companies or the same company. Putting a "safe" clear over a "problem" glaze will not automatically make the resulting glaze safe . . . you need to test it.

Thank you... I currently have one dish with a lemon and another with vinegar.

Note that those are only "rule in" tests not "rule out".

If they fail that test, you have no need to run a lab test. If they PASS that test, it does NOT say that it will not leach components. Only a standard acetic acid leach test will do that. (lab testing)

Note that if the glaze does not contain any toxics, then there is no need to test. It might be "bad" glass...... and deteriorate in visual character over time and use..... but it will not harm anyone.

best,

.......................john

John BaymoreImmediate Past President; Potters CouncilProfessor of Ceramics; New Hampshire Insitute of Art